High pressure and black clouds: Keynes and the frequentist theory of probability

The thesis of this paper is that Keynes wrote A Treatise onProbability in opposition to the frequentist theory of probability,systematised by John Venn, which denied any role for probabilityin decision theory. Keynes was interested in finding an alternativeconception of probability that could be utilised as a guideof life. To analyse this point, the paper considers Keynes'scriticisms of frequentist tradition in the two versions of hisFellowship dissertation, and in the published edition of hisTreatise. Keynes's project is then illustrated with the famousexample of whether or not to go out with one's umbrella in thesituation in which the pressure is high and the clouds are black.